I’m going to be a little controversial here… Whichever flavour of project management discipline you are following, having great Business Analysts and great Trainers on your project team is more important than having a great Project Managers.
A top notch BA will have gathered the best requirements and been instrumental in creating a realistic scope, and a top notch Trainer will give your staff the best education meaning the product will be used well by all and considered a success.
The BA and Trainer skill set is also very complimentary, and getting the people and relationships right will further increase your chances of delivering solid product creation, testing and delivery.
I am by no means saying that you don't need a PM or that you don't need a good one, but I have seen projects fail even with great PM’s at the helm. Generally because of poor BA performance on requirements gathering, and poor translation for the technical teams. I have also seen poor training ruin the implementation of solid products, and you are then faced with disgruntled users who will never really trust your product even if it does what it is supposed to.